Yes, 5/16 hose fits fine on the inlet side of the fuel supply pump.
Besides the restriction inside of the supply pump outlet the return line that comes out from the valve on the Fuel Injection Pump also has aprox. 1/4 inch I.D. hose. I also replaced that one with 1/4 rubber hose. So it is restricted on both ends at the supply pump and at the valve end to 1/4 inch.

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84 300D, 82 Volvo 244Gl Diesel